The present invention is directed to a method for transmitting information in a motor vehicle among electrical components of the motor vehicle. The components are connected to a data bus structure of the motor vehicle in order to transmit information and to a power line structure of the motor vehicle in order to be supplied with power. The information is transmitted via the data bus structure in successive cycles. Each cycle includes at least one time window for transmitting information at specific points in time and at least one event window for transmitting information in response to specific events.
The present invention is also directed to a method for transmitting information in a motor vehicle among electrical components of the motor vehicle, in that the information is transmitted, at least in part, both via the data bus structure as well as via the power line structure, in order to provide redundant information transmission.
In addition, the present invention is directed to a communications system for a motor vehicle. The communications system includes a plurality of electrical components, a data bus structure to which the components are connected in order to transmit information among the components, and a power supply structure to which the components are connected in order to be supplied with power. The information is transmitted over the data bus structure in successive cycles, each cycle including at least one time window for transmitting information at specific points in time and at least one event window for transmitting information in response to specific events.
The present invention is also directed to a communications system for a motor vehicle. The communications system includes a plurality of electrical components, a data bus structure to which the components are connected in order to transmit information among the components, and a power supply structure to which the components are connected in order to be supplied with power. In the communications system, the information is transmitted, at least in part, both via the data bus structure as well as via the power line structure.
In motor vehicles, electrical components are increasingly being used which communicate with one another via a data bus structure for purposes of transmitting information. The electrical components are connected to a power supply line structure in order to be supplied with power. The electrical components are sensors, actuators and/or control units, for example. Moreover, in motor vehicles, even those functions implemented using conventional methods, at least in part, as mechanical functions due to safety considerations or for other reasons, are increasingly being realized as electrical functions. For example, if previously the commands were transmitted from a gas pedal via a Bowden cable to a throttle valve or to a control unit of the internal combustion engine, today, this function is typically realized as an electronic function, a sensor recording the position of the gas pedal, a transducer converting the sensor signals into corresponding electrical signals, which are then transmitted via a data-transmission line to the throttle valve or to the control unit of the internal combustion engine and are further processed there. The control signals are retransmitted by the control unit to a fuel injection system and/or to gas exchange valves (intake/discharge valves) of the internal combustion engine. The actual activation of the throttle valve, of the injection system and/or of the gas exchange valves is handled by suitable actuators, which are driven by the control signals (so-called throttle-by-wire). All of the so-called X-by-wire functions, such as brake-by-wire, steer-by-wire, shift-by-wire, etc., work in a similar fashion in a motor vehicle, in which case, functions conventionally implemented, at least in part, as mechanical functions, are realized exclusively as electrical functions.
To keep the outlay for wiring among the individual electrical components in the motor vehicle to a minimum, the electrical components are typically interconnected via data bus structures, via which information, for example measurement signals, control signals, status information, etc., can be transmitted in accordance with specific communication protocols. Since the trend is for fewer and fewer motor vehicle functions to be implemented as mechanical functions, there is a marked increase, on the one hand, in the amount of information to be transmitted in the motor vehicle communications systems and, on the other hand, in the requirement for the security of the information transmitted over the data bus structure.
An important safety aspect to be considered when transmitting information in a motor vehicle is, on the one hand, that the information be transmitted at all events over the data bus structure and reach its receiver at all events and not be lost, for example due to an overloading of or a defect in the data bus structure, or by arriving at the wrong receiver. In order to allow for this safety requirement, in conventional communications systems for motor vehicles the information is not only transmitted over the data bus structure, but also redundantly over the power line structure. The transmission of information via the power line structure is also referred to as power line communications (PLC). The design and method of functioning of such communications systems, as well as the topology and the requisite conditioning of the power line structure are described in the German Patent Applications DE 101 42 408 A1, DE 101 42 409 A1 and DE 101 42 410 A1.
On the other hand, an important safety aspect is that the transmitted information not only reach the correct receiver with certainty, but also within a specifiable transmission time. To be able to fulfill this safety requirement, many different communication protocols have been developed in the past. Some of these are briefly described in the following.
Such a communication protocol for transmitting information within the framework of safety-critical applications is, for example, the Time Triggered Controller Area Network (TTCAN) protocol. The TTCAN protocol is based on the Controller Area Network (CAN) data link layer, which is specified in ISO 11898-1. The TTCAN protocol can make use of the standardized CAN physical layers, as are specified for high-speed transmitting/receiving units in ISO 11898-2 and for fault-tolerant, low-speed transmitting/receiving units in ISO 11898-3. The mechanisms provided by the TTCAN protocol render possible both the time-controlled, as well as the event-controlled transmission of messages. This enables CAN-based networks to be used in safety-critical environments (for example in a closed-loop control circuit). Another benefit derived from the TTCAN protocol is the improvement in the real-time performance in CAN-based networks.
The ISO (International Standardization Organization) has specified the TTCAN protocol in ISO 11898-4. In this specification, in one communication cycle (basic cycle), there are three different types of time frames during which messages can be transmitted: exclusive time windows, arbitrating time windows, and free time windows. In the arbitrating time windows, a plurality of messages can compete for access to the data bus structure. The exclusive time windows are assigned to a specific message, which is periodically transmitted to the data bus structure without competing for the access rights. Thus, the exclusive time windows correspond to the time windows along the lines of the present invention.
In order to be compatible with the time-controlled communication, all of the components (network nodes) have a common time base, which is made available either by an internal or an external timing element. An event-controlled information transmission in a manner characteristic of CAN is possible in the arbitrating time windows. Thus, this corresponds to the event windows in accordance with the present invention. The free time windows make it possible for the communications system to be subsequently expanded in a relatively simple manner. A cycle for transmitting information begins with a reference message which synchronizes the components. The automatic retransmission of those messages which had not been able to be successfully transmitted, as is characteristic of CAN, is deactivated.
In accordance with the TTCAN protocol, information is transmitted in periodically repeating cycles, each cycle having at least one time window (exclusive time window), in which specified messages are able to be transmitted at specific points in time within the cycle. Moreover, each cycle includes at least one event window (arbitrating time window) which can be used for an event-controlled transmission of information. Thus, in the case of the TTCAN protocol, an event-controlled approach is integrated into the time-controlled approach for data transmission of the CAN. This makes it possible for the communication employed in the TTCAN data bus structure to behave deterministically; i.e., for a conclusion to be reached regarding the transmission time of a message. Therefore, the TTCAN protocol is very well suited for use in safety-critical systems. Additional information on the TTCAN protocol can be obtained from a multiplicity of publications, for example on the Internet at http://212.114.78.132/can/ttcan/ including publications by Führer, T. et al.: “Time-Triggered Communication on CAN,” by Hartwich, F. et al.: “CAN Network With Time-Triggered Communication,” and by Fonseca, J. et al.: “Scheduling for a TTCAN Network with a Stochastic Optimization Algorithm.”
Another communication protocol, which is suited for use in safety-critical environments, is the FlexRay protocol. At the forefront of the FlexRay development were, above all, the requirements for a high data transmission rate, a deterministic communication, a high error tolerance and flexibility. In accordance with the FlexRay protocol, the information is transmitted in successive communication cycles. A shared understanding of time is provided in the electrical components (network nodes), the components being synchronized by reference messages (so-called SYNC messages) within one cycle. To render possible both a synchronous, as well as an asynchronous transmission of messages, the communication cycle is divided into a static segment and a dynamic segment, which each have at least one window (slot or time slot) for transmitting information.
The slots of the static segment are assigned to specific messages, which are periodically transmitted to the FlexRay data bus structure at specific points in time, without competing for the access rights. In this respect, the slots of the static segment correspond to the time windows along the lines of the present invention. An event-controlled information transmission can be realized in the slots of the dynamic segment. In this respect, the slots of the dynamic segment correspond to the event windows along the lines of the present invention.
While in accordance with the Time Division Multiple Access (TDMA) method, the FlexRay data bus structure is accessed during the static segment of the cycle, in accordance with the so-called Flexible Time Division Multiple Access (FTDMA) method, the bus structure is accessed during the dynamic segment of the cycle. A so-called minislotting method is used to access the data bus structure during the dynamic segment of the cycle. At the present time, there is still no standard, such as an ISO standard, for the FlexRay protocol. Details described here regarding the protocol could also possibly change in the future. Additional information on the FlexRay protocol can be obtained from the Internet at http://www.flexray.de, which includes, inter alia, several publications that are accessible to all.
Another communication protocol that is suited for safety-critical environments is the Time-Triggered Communication Protocol (TTP), in particular, version C (TTP/C) of this protocol. In the case of TTP, information is transmitted in successive cycles (rounds). Each cycle includes a plurality of windows (slots) for transmitting information. One portion of the windows is used for the guaranteed, deterministic transmission of real-time data. This portion of the windows (slot for state data) corresponds to the time windows along the lines of the present invention. Moreover, one portion of the window is reserved for event-controlled information transmission, the event-controlled messages being transmitted piggyback on the TTP data frame. This portion of the windows (slot for event data) corresponds to the event windows along the lines of the present invention. Additional information can be obtained on the Internet, on the home page of the firm TTTech Computertechnik AG, Vienna, Austria, at http://www.tttech.com/technology/articles.htm, which includes several publications on the subject of TTP that are accessible to all.
Within the framework of the so-called DISCO (Distributed Embeddable Systems for Control Applications) project at the University of Aveiro, Portugal, a new MAC (Medium Access Control) protocol was developed and designed as the FTT-CAN (Flexible Time-Triggered Controller Area Network) protocol. The FTT-CAN protocol is suited for use in safety-critical environments. The FTT-CAN protocol is very similar to the TTCAN protocol and is generally distinguished from it by the type of sequence coordination (so-called scheduling) of the information transmission. Also, in accordance with the FFT-CAN protocol, the information is transmitted in successive cycles, each cycle including time windows for the time-controlled transmission of information and event windows for the event-controlled transmission of information. The DISCO project involves many Portuguese research institutes, inter alia, the Instituto de Engenharia Elektronica e Telematica de Aveiro (IEETA) of the Universidade de Aveiro, Portugal. More detailed information on the FTT-CAN protocol can be obtained on the Internet, in particular from the publication Fonseca, J. A. et al.: DISCO-Distributed Embeddable Systems for Control Applications: Project Overview, at http://www.ieeta.pt/˜jaf/papers/ano2001/DISCO.pdf.
Another communication protocol for use in safety-critical environments is the Media Oriented Systems Transport (MOST) protocol, in which information is likewise transmitted in successive cycles (frames). Each cycle includes time windows (synchronous area) for the time-controlled transmission of information and event windows (asynchronous area) for the event-controlled transmission of information. Additional information on the MOST protocol can be obtained from the Internet, for example at http://www.mostcooperation.com, the MOST technology being explained in detail in many publications that are accessible to all.
In addition to the above specifically mentioned and briefly described communication protocols for use in safety-critical environments, there are still other communication protocols, or there will still be others in the future, in which the information is transmitted in successive cycles, each cycle including time windows for the time-controlled transmission of information and event windows for the event-controlled transmission of information, which are thus likewise suited for use in safety-critical systems.
Common to these communication protocols is the type of information transmission. For example, information that occurs at unpredictable points in time is transmitted in the event windows. Such information includes, for example, sensor measurement signals, alarm or error messages of a control unit, manually triggerable signals (signals for controlling comfort and convenience functions in the motor vehicle), etc. On the other hand, safety-critical and time-critical information is typically transmitted in the time windows of the cycles. This makes it possible to ensure that the transmitted information is transmitted within a specifiable transmission time and is also actually transmitted to the receiver and received by the same. For that reason, when working with the communication protocols for safety-critical applications, it is vitally important that precisely that information transmitted in the time windows also actually arrive at the receiver. A defect in the data bus structure, which could adversely affect or even entirely prevent a transmission of information, would have disastrous consequences for safety in the context of the safety-critical applications.
For that reason, in spite of damage to or failure of a data bus structure, a relatively substantial outlay is expended to nevertheless enable information to be transmitted among the components connected to the data bus structure. A multiple-redundant design of the data bus structure would be possible, for example. However, this is very complicated and expensive, since additional data bus structures, as well as additional transmitting/receiving units are required for connecting the components to the additional data bus structures. Another drawback inherent in motor vehicles in particular, is the additional space required for the additional data bus structures, as well as for the additional transmitting/receiving units of the components. This additionally required space is either not available in motor vehicles or could be made available more effectively to the motor vehicle occupants, either by increasing the size of the passenger compartment or of the trunk.